3-1 defer调用.mp4

func writeFile(filename string){
    file,err:=os.Create(filename)
    if err != nil {
        panic(err)
    }
    defer file.Close()
    writer:= bufio.NewWriter(file)
    defer writer.Flush()

    for i := 0; i < 20; i++ {
        fmt.Fprintln(writer,string(i))
    }
}

等我代码写完了,我就忘记这个了

所以我就进就加一个这个

package main

import (
    "bufio"
    "fmt"
    "os"
)

func tryDefer() {
    defer fmt.Println(2)
    defer fmt.Println(1)

    fmt.Println(3)
    fmt.Println(4)
}

func writeFile(filename string) {
    file, err := os.Create(filename)
    if err != nil {
        panic(err)
    }
    defer file.Close()
    writer := bufio.NewWriter(file)
    defer writer.Flush()

    for i := 0; i < 20; i++ {
        fmt.Fprintln(writer, i)
    }
}

func main() {
    writeFile("fib.txt")
}

3-2 错误处理概念.mp4

package main

import (
    "bufio"
    "fmt"
    "os"
)

func tryDefer() {
    defer fmt.Println(2)
    defer fmt.Println(1)

    fmt.Println(3)
    fmt.Println(4)
}

func writeFile(filename string) {
    file, err := os.Create(filename)
    if err != nil {
        panic(err)
    }
    defer file.Close()
    writer := bufio.NewWriter(file)
    defer writer.Flush()

    for i := 0; i < 20; i++ {
        fmt.Fprintln(writer, i)
    }
}

func writeFile2(filename string) {
    file, err := os.OpenFile(
        filename, os.O_EXCL|os.O_CREATE, 0666)
    if err != nil {
        panic(err)
    }
    defer file.Close()
    writer := bufio.NewWriter(file)
    defer writer.Flush()

    for i := 0; i < 20; i++ {
        fmt.Fprintln(writer, i)
    }
}

func main() {
    writeFile2("fib.txt")
    /**
    panic: open fib.txt: The file exists.

    goroutine 1 [running]:
    main.writeFile2({0xf7b58, 0xc000040000})
        E:/Projects/GolandProjects/go-camp/mooc/code/learngo/errhandling/defer/defer.go:35 +0x1d5
    main.main()
        E:/Projects/GolandProjects/go-camp/mooc/code/learngo/errhandling/defer/defer.go:47 +0x25

    Process finished with the exit code 2
     */
}

如果文件存在就报错

可以处理一下

func writeFile2(filename string) {
    file, err := os.OpenFile(
        filename, os.O_EXCL|os.O_CREATE, 0666)
    if err != nil {
        fmt.Println("flie already exist!!!")
        return
    }
    defer file.Close()
    writer := bufio.NewWriter(file)
    defer writer.Flush()

    for i := 0; i < 20; i++ {
        fmt.Fprintln(writer, i)
    }
}

真正的处理错误

func writeFile2(filename string) {
    file, err := os.OpenFile(
        filename, os.O_EXCL|os.O_CREATE, 0666)
    if err != nil {
        if pathError, ok := err.(*os.PathError); !ok {
            // 真的 不知道是森什么错了
            // 那就挂掉程序吧
            panic(err)
        } else {
            fmt.Printf("%s, %s, %s\n",
                pathError.Op,
                pathError.Path,
                pathError.Err,
            )
        }
        return
    }
    defer file.Close()
    writer := bufio.NewWriter(file)
    defer writer.Flush()

    for i := 0; i < 20; i++ {
        fmt.Fprintln(writer, i)
    }
}

3-3 服务器统一出错处理浏览器需放大.mp4

3-4 服务器统一出错处理.mp4

error vs panic

• 意料之中: 使用error . 如文件打不开
• 意料之外: 使用panic . 如数组越界

输入的参数类型是函数

输出的返回类型也是函数